The present disclosure relates to systems and methods for determining health parameters of energy storage cells and, more specifically, to self-discharge determination in energy storage cells (e.g., employed in rechargeable service), as well as systems including such cells.
Rechargeable batteries are used in many devices, including cars and portable consumer electronics. Demand for higher and higher energy density rechargeable batteries with smaller and smaller self-discharge in these devices, among other things, has brought lithium-ion batteries to prominence (lithium-ion batteries typically have relatively high energy density and relatively low self-discharge compared to most other known battery chemistries).
One drawback of lithium-ion batteries, however, is their potential to catch fire and/or explode. For example, internal soft short circuits (ISSCs) in a lithium-ion battery may develop, and may eventually transform into internal hard short circuits (IHSCs). Heat generated from elevated self-discharge current through IHSCs may cause unpredictable catastrophic failures due to thermal runaway of the lithium-ion battery, in which the battery may smoke (emitting toxic vapors), catch fire, explode, or combinations thereof. Aside from the safety issues resulting from these catastrophic failures in lithium-ion batteries, catastrophic failures have also resulted in large-scale recalls costing hundreds of millions of dollars and damaging provider reputations. As size of batteries in rechargeable battery systems increases (e.g., in electric drive vehicles), or stationary storage (e.g., grid storage) the concern for catastrophic failures also increases.
Formation of ISSCs and IHSCs may be accompanied by an increase in self-discharge of batteries. Conventional methods to measure self-discharge in batteries, however, are time intensive. Some of them require full charge-discharge cycling of the battery with long rest between charging and discharging operations, others use relatively long rest time to allow battery equilibration to a state of charge (SOC) of interest before measuring self-discharge. None of conventional methods use a pure self-discharge metric, which is separated from other parallel processes in the cell (e.g., redistribution of Li cations in the Li-ion battery due to faradaic and diffusion processes). These conventional methods are not practical for many applications because of the length of time required to perform them and uncertainty in self-discharge definitions and measurements. Furthermore, these conventional methods are generally only capable of detecting IHSCs, not ISSCs. Detection of IHSCs in batteries may be of limited value because catastrophic failures may be imminent and difficult or impossible to prevent by the time IHSCs form.